The present invention relates to flow control apparatus for use in fluid flow catheters of the type found in blood pressure and dynamics measurement systems. In such systems, a catheter commonly is inserted into a patient's vein to a location where measurements are desired. The catheter is maintained full of a neutral, sterile solution, which actually flows into the patient at a very low rate of, say, 3 ml/hr. This low flow is required to keep the catheter open, or patent, throughout its length, by preventing the ingress of blood constituents at the in-dwelling end of the catheter. By monitoring changes in the liquid pressure in the catheter, a variety of useful data can be obtained regarding the blood pressure, flow, etc. at the in-dwelling end.
When such catheters are prepared for use, they must be flushed completely of all air which could be harmful to the patient. Since the normal small flow rate would cause the device to fill very slowly, provisions have been made in the prior art for providing a second, much higher flow rate (perhaps 30 ml/min.) for use during initial flush and fill of the catheter and during use to momentarily allow a higher flow rate into the patient to clear out any debris which may have collected at the in-dwelling end of the catheter. U.S. Pat. No. 3,675,891, issued July 12, 1972 to Gordon S. Reynolds and others, discloses one prior art catheter flushing apparatus. The present invention embodies improvements upon the Reynolds device.